18 Questions
What is the common adverse effect associated with Phenobarbital?
Nausea and vomiting
Which of the following is a characteristic of Phenobarbital pharmacokinetics?
Long plasma half-life
What is the mechanism of action of Phenobarbital in the CNS?
Increases inhibitory neurotransmitters
Which of the following is a contraindication for Phenobarbital use?
Pregnancy
In what type of seizures is Phenobarbital commonly used?
Partial seizures
'Increases the inhibitory neurotransmitters (e.g: GABA ) and decreases the excitatory transmission' - This statement is associated with the mechanism of action of:
'Phenobarbital'
What is the mechanism of action of benzodiazepines?
Increasing chloride ion channel opening frequency
What is a common side effect of barbiturate overdose?
Tachycardia
Which barbiturate is associated with atonic and infantile spasms?
Phenobarbital
Which benzodiazepine is specifically used for absence seizures?
Clonazepam
What clinical use is associated with mephobarbital?
Infantile spasms
How do barbiturates affect the CNS and respiratory system during toxicity?
Induce Cheyne-Stokes respiration
What is the main route of excretion of Phenobarbital?
Urinary excretion
What is a common side effect associated with Phenobarbital toxicity?
Gastrointestinal upset
How does Phenobarbital affect the brain's GABA content?
Increases GABA content
In CNS disorders, Phenobarbital is particularly effective against which type of seizures?
Absence seizures
What is one of the mechanisms of action of barbiturates like Phenobarbital in the brain?
Facilitation of GABA activity
Which drug should not be given concomitantly with Phenobarbital due to its metabolism being inhibited by Phenobarbital?
Valproic Acid
Study Notes
Phenobarbital
- Mechanism of action: increases inhibitory neurotransmitters (e.g., GABA) and decreases excitatory transmission, prolongs the opening of Cl- channels, and blocks excitatory responses induced by glutamate
- Side effects: nausea, vomiting, GIT disturbances, increased appetite and weight gain, transient hair loss, hepatotoxicity, thrombocytopenia, and neural tube defects in offspring of women
- Pharmacokinetics: long-acting barbiturate, 20-45% protein-bound, low lipid solubility, and hepatic microsomal enzyme system metabolism
- Plasma half-life: 53-118 hours (adults), 60-180 hours (children and newborns)
- Uses: partial seizures and generalized tonic-clonic seizures, but little effect on absence, atonic, and infantile spasms
Benzodiazepines
Diazepam
- Mechanism of action: interacts with specific receptors on the GABAA receptor–chloride ion channel macromolecular complex
- Uses: generalized tonic-clonic and status epilepticus
- Pharmacokinetics: well-absorbed, widely distributed, extensively metabolized to many active metabolites
- Plasma binding: 95%
- Half-life: 20-40 hours
- Toxicity: sedation, drowsiness, and lethargy, strong inducing agent
Lorazepam
- Uses: status epilepticus
- Pharmacokinetics: rapidly and extensively distributed
- Plasma binding: 85%
- Half-life: 20-40 hours
Clonazepam
- Uses: absence seizures
- Pharmacokinetics: well-absorbed, widely distributed, extensively metabolized
- Plasma binding: 85%
- Half-life: 20-40 hours
Nitrazepam
- Uses: infantile spasms, myoclonic seizures
- Pharmacokinetics: well-absorbed, widely distributed, extensively metabolized
- Plasma binding: 80%
- Half-life: 20-40 hours
Clorazepate Dipotassium
- Uses: complex partial seizures
- Pharmacokinetics: well-absorbed, widely distributed, extensively metabolized
- Plasma binding: 90%
- Half-life: 20-40 hours
Carbamazepine
- Mechanism of action: interacts with voltage-gated Na+ channels, increases K+ conductance
- Pharmacokinetics: well-absorbed, widely distributed, extensively metabolized
- Plasma binding: 70-80%
- Half-life: 30 hours
- Toxicity: GI upset, drowsiness, ataxia, headache, diplopia, hepatotoxicity, congenital malformations, hyponatraemia, water intoxication, and late hypersensitivity reaction
Sodium Valproate (Valproic Acid)
- Mechanism of action: increases GABA content in the brain, attenuates Ca-mediated T current, and prolongs Na+ channel inactivation
- Pharmacokinetics: available as capsule, syrup, and IV, high oral bioavailability, inhibits metabolism of several drugs
- Plasma half-life: approximately 15 hours
- Clinical use: effective against absence, myoclonic, and generalized tonic-clonic seizures, less effective for partial seizures, and used for mania treatment
Learn about the toxicity effects of Phenobarbital, such as nausea, vomiting, weight gain, and hepatotoxicity. Understand how Phenobarbital increases inhibitory neurotransmitters and decreases excitatory transmission by prolonging the opening of Cl- channels. Explore its mechanism of action and potential neural tube defects in offspring.
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